Methods and apparatus for communicating and displaying compressed image data

ABSTRACT

Methods and apparatus are provided for creating one or more compressed image tiles based on a compressed file that describes a digital image. In particular, the compressed image tiles are created without fully decompressing the compressed file. Each compressed image tile includes data corresponding to a portion of the digital image, and is independent of other compressed image tiles (i.e., may be decompressed without decompressing any other tile). In response to requests to display a desired portion of the digital image at a specific resolution, the compressed image tiles corresponding to the desired portion and the specified resolution are communicated via a band limited communication channel. In this regard, the portions of the digital image may be quickly communicated and displayed, without having to wait for the entire compressed file to be communicated over the band limited channel.

BACKGROUND

This invention relates to apparatus and methods for communicating anddisplaying image data, and more particularly relates to apparatus andmethods for communicating and displaying compressed image data.

As digital image processing technology has advanced in recent years,documents and images are increasingly being created, stored anddisplayed electronically. Indeed, commonly available computer programssuch as word processors, page layout, graphics arts, photo editing andother similar programs may be used to create, edit, save and displayelectronic documents and images (collectively referred to as “electronicdocuments”). In addition, commonly used electronic devices such asdigital scanners, digital copiers and digital cameras may be used tocreate and save electronic documents. As a result, the number ofelectronic documents that are created each year grows at an extremelyrapid rate.

Further, improvements in image processing technology have resulted insignificant improvements in electronic document image quality. Indeed,electronic images are frequently created at resolutions of 1200 dots perinch (“dpi”) or more. As image resolution has increased, the amount ofdata required to represent high quality images also has increased. Forexample, a single page containing an 8″×10″ image having four colorseparations (e.g., cyan, magenta, yellow and black) and a resolution of1200 dpi includes more than 109 mega-pixels for each color separation,and may include more than 436 mega-bytes (“MB”) of data.

Because of the large amount of data required to represent high qualityimages, it is not practical to store such information in an uncompressedstate. Thus, applications and devices that create and store high qualitydigital color images typically do so in a compressed format. Inparticular, as a result of the development of block compressionstandards such as JPEG (an acronym for “Joint Photographic ExpertsGroup”), many digital imaging systems and applications create, convert,and/or maintain digital content in a JPEG compressed format (referred toherein as “JPEG data”). Depending on the image, it often is possible toachieve very high compression ratios. For example, the image describedabove that includes 436 MB of uncompressed data may be compressible toapproximately 40 MB of JPEG data.

One such digital imaging system that converts and maintains digitalcontent in compressed form is a digital printing system, an example ofwhich is illustrated in FIG. 1. In particular, digital printing system10 includes document source 12, print server 14, client computer 16 andprinter 18. Document source 12 may be a personal computer, colorscanner, electronic document archive, or other source of electronicdocuments 20, and print server 14 may be a conventional print server,such as those manufactured by Electronics for Imaging, Inc. (FosterCity, Calif.) under the trademarks Fiery®, EDOX® and Splash®. Documentsource 12 provides electronic document 20 to print server 14 forprinting on printer 18.

Electronic document 20 may include data in a page description language(“PDL”), such as PostScript, portable document format (“PDF”), pagecommand language (“PCL”) or other PDL. Print server 14 includes rasterimage processor (“RIP”) 22 that converts electronic document 20 from PDLformat to raster data in a compressed format. For example RIP 22 mayconvert the PDF data to block-compressed raster data (e.g., JPEG data)in compressed file 24, which may be stored in memory 26. To print theelectronic document, RIP 22 may retrieve compressed file 24 from memory26, decompress the file, and provide the decompressed raster data toprinter 18 for printing.

Prior to printing, it often is desirable to display all or part of theraster image data contained in compressed file 24. For example, it maybe desirable to display all or part of compressed file 24 on clientcomputer 16 to visually proof the raster image data. Client computer 16may be part of print server 14, or may be separate from print server 14.For example, print server 14 may be located at a printshop, and clientcomputer 16 may be located at a customer office. Client computer 16 maycommunicate with print server 14 via communication channel 28, such as alocal area network, wide area network, the Internet, or other similarnetwork. Depending on the size of compressed file 24 and the bandwidthof communication channel 28, however, it may be impractically slow totransfer compressed file 24 to client computer 16 for display. Forexample, if compressed file 24 is a 40 MB file, and communicationchannel 28 is a conventional digital subscriber line (“DSL”) or cablebroadband connection, it may take more than ninety seconds or more todownload and display the file on client computer 16.

To solve this bandwidth problem, some previously known digital printingsystems create a reduced resolution (often referred to as a “thumbnail”)image of the raster image data, and then transfer only the thumbnailimage to client computer 16. Because the file size of the thumbnailimage is much smaller than the size of compressed file 24, the downloadtime is much faster than that required to transmit the entire compressedimage file. Although the thumbnail image may be useful for verifyingvery general qualities of the image in compressed file 24, theresolution of the thumbnail image is typically insufficient for proofingpurposes. Further, because the resolution of the thumbnail image isfixed, a user cannot zoom in or out to view the image at multipleresolutions.

Another previously known digital imaging system attempts to solve thelimited bandwidth problem by encoding and communicating only a subset ofhigh resolution image data. For example, Dekel et al. U.S. Pat. No.6,314,452 (“Dekel”) describes an imaging system that includes a serverthat encodes a region of interest (“ROI”) of an uncompressed image, andthen transmits only the compressed ROI data to a remote client computervia a communication network. This previously known technique assumesthat a desired ROI is less than the entire image, and therefore theserver only compresses and communicates data associated with the ROI.One problem with this technique, however, is that all of the image dataare never entirely compressed. As a result, such systems areincompatible with digital imaging systems, such as digital printingsystem 10, that include print servers that compress and store all of theraster image data. In addition, because the Dekel system nevercompresses an entire image, the system requires very large storagedevices.

In view of the foregoing, it would be desirable to provide methods andapparatus that allow fast communication and display of compressed rasterimage data.

It further would be desirable to provide methods and apparatus thatallow fast communication and display of compressed raster image data atfull resolution.

It additionally would be desirable to provide methods and apparatus thatallow fast communication and display of compressed raster image data atmultiple resolutions.

It also would be desirable to provide methods and apparatus that allowfast communication and display of raster image data that has been fullycompressed.

SUMMARY

In view of the foregoing, it is an object of this invention to providemethods and apparatus that allow fast communication and display ofcompressed raster image data.

It further is an object of this invention to provide methods andapparatus that allow fast communication and display of compressed rasterimage data at full resolution.

It additionally is an object of this invention to provide methods andapparatus that allow fast communication and display of compressed rasterimage data at multiple resolutions.

It also is an object of this invention to provide methods and apparatusthat allow fast communication and display of raster image data that hasbeen fully compressed.

These and other objects of this invention are accomplished by providinga tile server that communicates with a client device via a band limitedcommunication channel. The tile server creates one or more compressedimage tiles based on a compressed file that describes a digital image.In particular, the tile server creates the compressed image tileswithout fully decompressing the compressed file. Each compressed imagetile includes data corresponding to a portion of the digital image, andis independent of other compressed image tiles (i.e., may bedecompressed without decompressing any other tile). In response torequests from a viewer application running on the client device todisplay a desired portion of the digital image at a specific resolution,the tile server provides compressed image tiles corresponding to thedesired portion and the specified resolution to the viewer applicationvia the communication channel. In this regard, the client device mayquickly receive and display portions of the digital image, withouthaving to wait for the entire compressed file to be communicated overthe band limited channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and features of the present invention can bemore clearly understood from the following detailed descriptionconsidered in conjunction with the following drawings, in which the samereference numerals denote the same elements throughout, and in which:

FIG. 1 is a block diagram of a previously known digital printing system;

FIG. 2 is a block diagram of an exemplary embodiment of a digitalprinting system in accordance with this invention;

FIG. 3 is an exemplary digital image for use with methods and apparatusin accordance with this invention;

FIG. 4 is an exemplary block compression technique for use with methodsand apparatus in accordance with this invention;

FIG. 5 is a depiction of exemplary portions of the digital image of FIG.3;

FIGS. 6A-6C are exemplary tiled representations of the digital image ofFIG. 3;

FIG. 7 is an exemplary tile from the tiled representation of FIG. 6A;

FIG. 8 is an exemplary process for creating compressed image tiles inaccordance with this invention;

FIG. 9 illustrates exemplary adjacent data blocks from the tiledrepresentation of FIG. 6A; and

FIG. 10 is a diagram illustrating an exemplary process for eliminatingintra-tile dependencies in accordance with this invention.

DETAILED DESCRIPTION

Referring to FIG. 2, an exemplary digital imaging system in accordancewith this invention is described. Digital imaging system 10′ includesprint server 14′ and client 16′, which includes viewer application 32,display device 34 and cache 36. Print server 14′ may be a Fiery, EDOX orSplash print server, or other similar device, and includes tile server30. In response to a request by a user of client 16′ to display thedigital image described in compressed file 24, tile server 30 createsone or more compressed image tiles 38 ₁′, 38 ₂′, . . . , 38 _(n)′ basedon compressed file 24, wherein each compressed image tile includes datacorresponding to a portion of the digital image. In particular, tileserver 30 creates one or more compressed image tiles 38 ₁′, 38 ₂′, . . ., 38 _(n)′ without fully decompressing compressed file 24. Moreover,each compressed image tile 38′ is independent (i.e., may be decompressedwithout decompressing any other tile). In response to requests fromviewer application 32 to display a desired portion of the digital imageat a specific resolution, tile server 30 provides compressed image tiles38′ that correspond to the desired portion and the specified resolutionto client 16′ via communication channel 28 for display on display device34. In this regard, client 16′ may quickly receive and display portionsof the digital image, without having to wait for the entire compressedfile to be received from print server 14′.

Referring now to FIGS. 2 and 3, an exemplary digital image is describedfor use with methods and apparatus in accordance with this invention.Digital image 40 may be included in electronic document 20, which may besent by document source 12 to print server 14′. RIP 22 may then convertand store electronic document 20 as compressed raster data in compressedfile 24. For example, RIP 22 may compress digital image 40 using a blockcompression technique, such as JPEG compression. In raster form, digitalimage 40 includes an array of pixels (e.g., a 4512×3584 array ofpixels).

An exemplary JPEG compression technique 50 that may be used by RIP 22 tocompress digital image 40 is illustrated in FIG. 4. At stage 52,uncompressed raster (pixel) data are grouped into blocks, with eachblock including an 8×8 array of pixels. At step 54, the pixel data ineach block are transformed using a discrete cosine transformation(“DCT”) to form an 8×8 array of DCT coefficients. At step 56, thecoefficients in each block are quantized. Finally, at step 58, thequantized DCT coefficients are encoded using Huffman encoding to formcompressed data. Persons of ordinary skill in the art will understandthat RIP 22 may use other similar block compression techniques tocompress digital image 40.

Referring again to FIG. 2, a user of client 16′ may want to display allor a portion of digital image 40 on display device 34, which may be acathode ray tube, liquid crystal display, plasma display, or othersimilar display device. For example, a user may wish to proof digitalimage 40 prior to printing the image on printer 18. To do so, it may bedesirable to display digital image 40 on display device 34. At fullresolution (i.e., 1:1), only a portion of the image may be visible onthe display. For example, as illustrated in FIG. 5, if digital image 40includes 4512×3584 pixels, and display device 34 includes 1024×768pixels, at full resolution, display device 34 displays a portion ofdigital image 40, such as portion 60 a. In contrast, at lowerresolutions (e.g., 1:2, 1:4), display device 34 may display largerportions of digital image 40, such as portions 60 b and 60 c.

Referring again to FIG. 2, in response to a request by a user of client16′ to display a desired portion (e.g., 60 a, 60 b or 60 c) of digitalimage 40 on display device 34, tile server 30 may divide digital image40 into a plurality of tiles, in which each tile includes a subset ofthe pixels of the entire image, tile server 30 may identify the tilescorresponding to desired portion, and may then communicate pixel datafor the identified tiles to client 16′ and displayed on display device34. For improved efficiency, tile server 30 may compress the tiles priorto communication. In particular, tile server 30 may create one or morecompressed image tiles 38′ based on compressed file 24, wherein eachcompressed image tile 38′ includes compressed data corresponding to aportion of the digital image described in compressed file 24. Tileserver 30 may then communicate compressed image tiles 38′ correspondingto the desired portion to client 16′, which may decompress the tiles anddisplay the data on display device 34.

To further improve efficiency, tile server 30 may create compressedimage tiles 38′ without fully decompressing compressed file 24. Further,tile server 30 may create compressed image tiles 38′ that areindependent (i.e., may be decompressed without decompressing any othertile). To facilitate an understanding of this invention, the followingsections first describe image tiling of uncompressed image data, andthen describe methods in accordance with this invention for creatingindependent compressed image tiles 38′ without fully decompressingcompressed file 24.

Exemplary tiled representations of a digital image 40 are illustrated inFIGS. 6A-6C. In particular, FIG. 6A illustrates digital image 40 dividedinto fourteen rows R₁-R₁₄ and eighteen columns C₁-C₁₈ of uncompressedtiles 38 ₁ at a first resolution (e.g., 1:1), FIG. 6B illustratesdigital image 40 divided into seven rows R₁-R₇ and nine columns C₁-C₉ ofuncompressed tiles 38 ₂ at a second resolution (e.g., 1:2), and FIG. 6Cillustrates digital image 40 divided into four rows R₁-R₄ and fivecolumns C₁-C₅ of uncompressed tiles 38 ₂ at a third resolution (e.g.,1:4). Tiles 38 ₁, 38 ₂ and 38 ₃ may be aligned with reference to leftand top edges 42 a and 42 b, respectively, of digital image 40. Personsof ordinary skill in the art will understand that digital image 40 maybe divided into additional uncompressed tiles 38 ₄, 38 ₅, . . . , 38_(n), at additional resolutions.

Each of tiles 38 ₁, 38 ₂ and 38 ₃ includes a predetermined number ofpixels. For example, each of tiles 38 ₁, 38 ₂ and 38 ₃ may include a256×256 array of pixels. As described above in connection with FIG. 4,during the compression process, pixels in digital image 40 may begrouped into blocks, with each block including a certain number ofpixels. For example, as illustrated in FIG. 7, each 256×256 uncompressedtile 38, may include a 32×32 array of blocks 70, with each block 70including an 8×8 array of pixels. Persons of ordinary skill in the artwill understand that tiles 38 ₁, 38 ₂ and 38 ₃ may include more than orless than 256×256 pixels, that the pixels in each tile may be groupedinto more than or less than 32×32 arrays of blocks 70, and that eachblock 70 may include more than or less than 8×8 arrays of pixels.

Referring again to FIG. 2, tile server 30 may create sets of compressedimage tiles 38 ₁′, 38 ₂′, . . . 38 _(n)′, each of which includes one ormore compressed data tiles associated with a corresponding one ofuncompressed image tiles 38 ₁, 38 ₂, . . . , 38 _(n), respectively.Referring now to FIG. 8, an exemplary process for creating sets ofcompressed image tiles 38 ₁′, 38 ₂′, . . . 38 _(n)′, is described.Beginning at step 80, tile server 30 retrieves compressed file 24 frommemory 26. Next, at step 82, tile server 30 decodes compressed file 24to recover quantized DCT block data. Next, at step 84, tile server 30identifies the blocks associated with each full-resolution tile 38 ₁.For example, referring to FIG. 6A, tile server 30 determines that thefirst 32×32 array of blocks is associated with tile 38 ₁ at row R₁,column C₁, the second 32×32 array of blocks is associated with tile 38 ₁at row R₁, column C₂, and so on. Referring again to FIG. 8, at step 86,tile server 30 modifies block data to eliminate intra-tile dependencies,described in more detail below. At step 88, tile server 30 calculatesblock data for lower-resolution tiles 38 ₂, 38 ₃, . . . , 38 _(n), basedon the modified block data for full-resolution tiles 38 ₁. Finally, atstep 90, tile server 30 re-encodes the modified block data to createsets of compressed image tiles 38 ₁′, 38 ₂′, . . . 38 _(n)′.

An example of intra-tile dependencies referred to in connection withstep 86 is described with reference to FIG. 9. In particular, FIG. 9illustrates exemplary adjacent DCT blocks 70 _(a)′ and 70 _(b)′, whichwere recovered by decoding data from compressed file 24. DCT block 70_(a)′ is associated with a first compressed image tile 38 _(1a)′, andDCT block 70 _(b)′ is associated with a second compressed image tile 38_(1b)′. DCT block 70 _(a)′ includes an 8×8 array of DCT coefficientsa₁₁-a₈₈, and DCT block 70 _(b)′ includes an 8×8 array of DCTcoefficients b₁₁-b₈₈. For JPEG-encoded data, the first coefficient ineach DCT block 70′, referred to as the “DC component” of the block,depends on the DC component of the immediately preceding (i.e.,leftmost) DCT block 70′ in the same row. In particular, the DC componentof a DCT block equals the difference between the actual DC value of theblock and the actual DC value of the immediately preceding block. Forexample, the DC component of DCT block 70 _(b)′ is coefficient b₁₁, andthe DC component of DCT block 70 _(a)′ is coefficient a₁₁. Coefficientb₁₁ equals the difference between the actual DC value of DCT block 70_(b)′ and the actual DC value of DCT block 70 _(a)′.

Thus, to eliminate intra-tile dependencies as specified at step 86 ofFIG. 8, tile server 30 scans the recovered block data, row by row, andmodifies the DC components of DCT blocks 70′ in the first column of eachtile to eliminate any dependence on the DC components of correspondingDCT blocks 70′ in the immediately preceding tile in the same row. Anexample of this process is described with reference to FIG. 10. Inparticular, tile 38 _(1c)′, which is adjacent left edge 42 a of digitalimage 40, includes thirty-two rows R₁-R₃₂ and thirty-two columns C₁-C₃₂of DCT blocks 70 _(c)′. Tile 38 _(1d)′, which is adjacent tile 38_(1c)′, includes thirty-two rows R₁-R₃₂ and thirty-two columns C₁-C₃₂ ofDCT blocks 70 _(d)′. Similarly, tile 38 _(1e)′, which is adjacent tile38 _(1d)′, includes thirty-two rows R₁-R₃₂ and thirty-two columns C₁-C₃₂of DCT blocks 70 _(c)′. DCT blocks 70 _(c)′, 70 _(d)′ and 70 _(c)′ eachinclude DC components (first coefficients) c₁₁, d₁₁ and e₁₁,respectively.

Because no tile precedes tile 38 _(1c)′ in the same row, none ofcoefficients c₁₁ of DCT blocks 70 _(c)′ in column C₁ of tile 38 _(1c)′require modification. Thus, tile server 30 does not modify anycoefficients in tile 38 _(c)′. Because tile 38 _(c)′ precedes tile 38_(1d)′ in the same row, however, tile server 30 modifies the DCcomponents of DCT blocks 70 _(d)′ of column C₁ of tile 38 _(1d)′ toeliminate dependence on the DC components of corresponding DCT blocks 70_(c)′ in tile 38 _(1c)′. In particular, for DCT block 70 _(d)′ in rowR₁, column C₁ of tile 38 _(1d)′, tile server 30 replaces coefficient d₁₁with the actual DC value of the block, which equals the sum ofcoefficients c₁₁ of each block 70 _(c)′ in row R₁ of tile 38 _(1c)′.Similarly, for DCT block 70 _(d)′ in row R₂, column C₁ of tile 38_(1d)′, tile server 30 replaces coefficient d₁₁ with the actual DC valueof the block, which equals the sum of coefficients c₁₁ of each block 70_(c)′ in row R₂ of tile 38 _(1c)′. This process continues for all otherDCT blocks 70 _(d)′ in column C₁ of tile 38 _(1d)′.

After eliminating the dependence of tile 38 _(1d)′ on tile 38 _(1c)′,tile server 30 next modifies tile 38 _(1e)′. Because tile 38 _(1d)′precedes tile 38 _(1e)′ in the same row, tile server 30 modifies the DCcomponents of DCT blocks 70 _(e)′ in column C₁ of tile 38 _(1e)′ toeliminate dependence on the DC components of corresponding DCT blocks 70_(d)′ in tile 38 _(1d)′. In particular, for DCT block 70 _(e)′ in rowR₁, column C₁ of tile 38 _(1e)′, tile server 30 replaces coefficient e₁₁with the actual DC value of the block, which equals the sum ofcoefficients d₁₁ of each block 70 _(d)′ in row R₁ of tile 38 _(1d)′.Similarly, for DCT block 70 _(e)′ in row R₂, column C₁ of tile 38_(1e)′, tile server 30 replaces coefficient e₁₁ with the actual DC valueof the block, which equals the sum of coefficients d₁₁ of each block 70_(d)′ in row R₂ of tile 38 _(1d)′. The process continues for all otherDCT blocks 70 _(e)′ in column C₁ of tile 38 _(1e)′. Tile server 30repeats this process for each row of tiles for the entire digital image40.

Referring again to FIG. 8, at step 88, tile server 30 calculates blockdata for lower-resolution tiles 38 ₂, . . . , 38 _(n), based on themodified block data for full-resolution tiles 38 ₁. To do so, tileserver 30 may calculate block data for tiles 38 ₂, . . . , 38 _(n) byaveraging the modified block data for tiles 38 ₁. For example, tileserver 30 may calculate block data for tile 38 ₂ in row R₁, column C₁ ofFIG. 6B by averaging block data of tiles 38 ₁ in rows R₁-R₂, columnsC₁-C₂ of FIG. 6A. Likewise, tile server 30 may calculate block data fortile 38 ₂ in row R₁, column C₂ of FIG. 6B by averaging block data oftiles 38 ₁ in rows R₁-R₂, columns C₃-C₄ of FIG. 6A, and so on, until allblock data for tiles 38 ₂ have been calculated. In a similar fashion,tile server 30 may calculate block data for tile 38 ₃ in row R₁, columnC₁ of FIG. 6C by averaging block data of tiles 38 ₂ in rows R₁-R₂,columns C₁-C₂ of FIG. 6B, and so on, until all block data for tiles 38 ₃have been calculated. Tile server 30 may calculate block data for tiles38 ₄, . . . , 38 _(n) in a similar fashion. Referring again to FIG. 8,at step 90, tile server 30 encodes the modified blocks for each set oftiles to create sets of independent compressed data tiles 38 ₁′, 38 ₂′,. . . , 38 _(n)′.

Referring again to FIG. 2, after creating sets of independent compresseddata tiles 38 ₁′, 38 ₂′, 38 ₃ ′, . . . , 38 _(n)′, tile server 30 mayprovide the tiles to client 16′ for displaying raster data. Inparticular, to display a portion of uncompressed raster image data,viewer application 32 requests one or more compressed image tiles 38′from tile server 30. In response, tile server 30 sends the requestedtiles via communication channel 28, which may be a wired network,wireless network, local area network, wide area network, the Internet orother similar network or combination of such networks. Because eachcompressed image tile 38′ represents only a portion of the originaluncompressed raster data, the compressed image tiles are smaller thancompressed file 24, and therefore require less time to communicate viacommunication channel 28.

For example, referring to FIGS. 2 and 6A, viewer application 32 mayrequest compressed image tiles 38 ₁ ′ for displaying portion 60 a ondisplay device 34. In response, tile server 30 sends viewer application32 the compressed image tiles 38 ₁′ associated with portion 60 a ofdigital image 40 (i.e., compressed image tiles 38 ₁′ in rows R₂-R₅ andcolumns C₆-C₁₀). Viewer application 32 decompresses the receivedcompressed image tiles 38 ₁′, and displays the decompressed data ondisplay device 34. In addition, viewer application 32 may store thereceived compressed image tiles 38 ₁′ in cache 36, which may be randomaccess memory (“RAM”), magnetic memory, optical memory, or other similarmemory or combination of such memory. Tile server 30 and viewerapplication 32 therefore may be used to quickly display a portion ofdecompressed raster data, without requiring image processor 14′ to fullydecompress compressed file 24, or communicate the entire compressed fileto client 16′.

In addition to sending the compressed image tiles 38 ₁′ associated withportion 60 a, tile server 30 also may send additional compressed imagetiles 38 ₁ ′ to viewer application 32. For example, after sending thecompressed image tiles 38 ₁′ associated with portion 60 a, tile server30 may then begin sending compressed image tiles 38 ₁′ that areassociated with portions of digital image 40 that immediately surroundportion 60 a (e.g., compressed image tiles 38 ₁′ in rows R₁ and R₆,columns C₅-C₁₁, and rows R₁-R₆ of columns C₅ and C₁₁). Viewerapplication 32 may store these additional compressed image tiles incache 36. In this regard, if a user wants to pan across digital image 40to view areas immediately surrounding portion 60 a, viewer application32 may quickly retrieve from cache 36 compressed image tiles 38 ₁′ thatare associated with the surrounding areas, decompress the data containedtherein, and display the decompressed data on display device 34.

In addition, tile server 30 may send lower-resolution compressed imagetiles 38 ₂′, 38 ₃ ′, . . . , 38 _(n)′ to viewer application 32, whichmay store these additional compressed image tiles in cache 36. Viewerapplication 32 may utilize the lower-resolution tiles to allow a user tozoom in or out of the image. For example, after viewing portion 62 a, auser may wish to zoom out to display portion 62 b, and then zoom outagain to display portion 62 c, and so on. To display a portion 62 b or62 c of digital image 40 at a particular resolution, viewer application32 may then retrieve the compressed image tiles 38′ associated with theportion from cache 36, decompresses the retrieved compressed tiles, anddisplay the decompressed data on display device 34.

Tile server 30 may continue sending compressed image tiles 38′ ofdigital image 40 to cache 36 until all remaining compressed image tiles38′ have been sent. At that point, viewer application 32 may quicklyretrieve compressed data for any portion and any resolution of digitalimage 40 directly from cache 36. Thus, tile server 30 and viewerapplication 32 may be used to quickly display decompressed raster dataat multiple resolutions, without requiring that image processor 14′fully decompress compressed file 24, or communicate the entirecompressed file to client 16′.

Persons of ordinary skill in the art will understand that the sequencethat tile server 30 uses to send compressed image tiles 38 ₁′, 38 ₂′, .. . , 38 _(n)′ to viewer application 32 may be changed. For example, ifviewer application 32 initially requests compressed image tiles fordisplaying portion 60 c on display device 34, tile server 30 may respondby first sending viewer application 32 the compressed image tiles 38 ₃′associated with portion 60 c (i.e., compressed image tiles 38 ₃′ in rowsR₁-R₄ and columns C₁-C₅), then sending compressed image tiles 38 ₂′associated with portion 60 b, and finally sending compressed image tiles38 ₁′ associated with portion 60 a. In this regard, a user may firstdisplay digital image 40 at low resolution, and then progressively zoomin to view portions of the image at higher resolutions.

The foregoing merely illustrates the principles of this invention, andvarious modifications can be made by persons of ordinary skill in theart without departing from the scope of this invention.

1. A system for processing a compressed image file that describes animage, the system comprising: a first computer adapted to create acompressed image tile based on the compressed image file without fullydecompressing the compressed image file, the compressed image tiledescribing a portion of the image; a second computer adapted todecompress the compressed image tile and display the portion of theimage.
 2. The system of claim 1, wherein the first computer comprises aprint server.
 3. The system of claim 1, wherein the second computercomprises a client computer.
 4. The system of claim 1, wherein the firstand second computer comprise the same computer.
 5. The system of claim1, wherein the compressed image file comprises data compressed accordingto a block compression standard.
 6. The system of claim 5, wherein theblock compression standard comprises a Joint Photographic Experts Groupcompression standard.
 7. The system of claim 1, wherein the compressedimage tile comprises image data at a first resolution.
 8. The system ofclaim 7, wherein the first resolution comprises full resolution.
 9. Thesystem of claim 1, wherein the first computer is adapted to create firstand second compressed image tiles based on the compressed image filewithout fully decompressing the compressed image file, the firstcompressed image tile describing a first portion of the image, and thesecond compressed image tile describing a second portion of the image.10. The system of claim 9, wherein the first compressed image tilecomprises image data at a first resolution, and the second compressedimage tile comprises image data at a second resolution.
 11. The systemof claim 9, wherein the first compressed image tile may be decompressedwithout decompressing the second compressed image tile.
 12. A system forprocessing a compressed image file that describes an image, the systemcomprising: a print server adapted to create a compressed image tilebased on the compressed image file without fully decompressing thecompressed image file, the compressed image tile describing a portion ofthe image; a client computer coupled to the print server via acommunication channel, the client computer adapted to receive thecompressed image tile from the print server via the communicationchannel, decompress the compressed image tile and display the portion ofthe image.
 13. The system of claim 12, wherein the compressed image filecomprises data compressed according to a block compression standard. 14.The system of claim 13, wherein the block compression standard comprisesa Joint Photographic Experts Group compression standard.
 15. The systemof claim 12, wherein the compressed image tile comprises image data at afirst resolution.
 16. The system of claim 15, wherein the firstresolution comprises full resolution.
 17. The system of claim 12,wherein the print server is adapted to create first and secondcompressed image tiles based on the compressed image file without fullydecompressing the compressed image file, the first compressed image tiledescribing a first portion of the image, and the second compressed imagetile describing a second portion of the image.
 18. The system of claim17, wherein the first compressed image tile comprises image data at afirst resolution, and the second compressed image tile comprises imagedata at a second resolution.
 19. The system of claim 17, wherein thefirst compressed image tile may be decompressed without decompressingthe second compressed image tile.
 20. A system for processing acompressed image file that describes an image, the system comprising: afirst computer adapted to create a plurality of compressed image tilesbased on the compressed image file without fully decompressing thecompressed image file, each compressed image tile describing acorresponding portion of the image; a second computer adapted todecompress the compressed image tiles and display the portions of theimage.
 21. The system of claim 20, wherein the first computer comprisesa print server.
 22. The system of claim 20, wherein the second computercomprises a client computer.
 23. The system of claim 20, wherein thefirst and second computer comprise the same computer.
 24. The system ofclaim 20, wherein the compressed image file comprises data compressedaccording to a block compression standard.
 25. The system of claim 24,wherein the block compression standard comprises a Joint PhotographicExperts Group compression standard.
 26. The system of claim 20, whereinthe compressed image tiles comprise image data at a first resolution.27. The system of claim 26, wherein the first resolution comprises fullresolution.
 28. A method for processing a compressed image file thatdescribes an image, the method comprising: creating a compressed imagetile based on the compressed image file without fully decompressing thecompressed image file, the compressed image tile describing a portion ofthe image; decompressing the compressed image tile and display theportion of the image.
 29. The method of claim 28, wherein the compressedimage file comprises data compressed according to a block compressionstandard.
 30. The method of claim 28, wherein the block compressionstandard comprises a Joint Photographic Experts Group compressionstandard.
 31. The method of claim 28, wherein the compressed image tilecomprises image data at a first resolution.
 32. The method of claim 31,wherein the first resolution comprises full resolution.
 33. The methodof claim 28, wherein creating further comprises creating first andsecond compressed image tiles based on the compressed image file withoutfully decompressing the compressed image file, the first compressedimage tile describing a first portion of the image, and the secondcompressed image tile describing a second portion of the image.
 34. Themethod of claim 32, wherein the first compressed image tile comprisesimage data at a first resolution, and the second compressed image tilecomprises image data at a second resolution.
 35. The system of claim 32,wherein the first compressed image tile may be decompressed withoutdecompressing the second compressed image tile.
 36. A method forprocessing a compressed image file that describes an image, the methodcomprising: creating a plurality of compressed image tiles based on thecompressed image file without fully decompressing the compressed imagefile, each compressed image tile describing a corresponding portion ofthe image; decompressing the compressed image tiles and display theportions of the image.
 37. The method of claim 36, wherein thecompressed image file comprises data compressed according to a blockcompression standard.
 38. The method of claim 37, wherein the blockcompression standard comprises a Joint Photographic Experts Groupcompression standard.
 39. The method of claim 36, wherein the compressedimage tiles comprise image data at a first resolution.
 40. The method ofclaim 39, wherein the first resolution comprises full resolution.